A coiled coil is a structural motif in proteins, in which alpha-helices are coiled together like the strands of a rope. Coiled coil domains are abundant in natural proteins (1, 2), and they may be the commonest method in nature of oligomerising proteins. Coiled-coils consist of two or more alpha-helices winding around each other in a supercoil, a simple yet versatile protein fold (3). A typical coiled-coil primary sequence is repetitive, made of seven-residue repeats called a ‘heptad’.
Many coiled coil type proteins are involved in important biological functions. Of particular interest herein, are those found in antigens or in carrier proteins.
Examples of coiled coils found in antigens include, but are not limited to:                i) the dimeric coiled coils found in the OCA family (where OCA means oligomeric coiled coil adhesion): examples are NadA, a Neisseria meningitidis protective antigen (4); YadA from Yersinia enterocolitica (5); UspA2 from Moraxella catarrhalis (6); BadA from Bartonella henselae (7) and HadA from Haemophilus influenzae (8).        ii) the trimeric coiled coils found in, amongst others, the influenza hemagglutinin HA2 protein (9), the F glycoprotein of Respiratory Syncytial virus (10), the gp41 glycoproteins of HIV-1 (11) and HIV-2 (12), and gp1,2 of Ebolavirus (13).        iii) the tetrameric coiled coils found in the Newcastle Disease FIN (hemagglutinin-neuraminidase) glycoprotein and other paramyxoviruses (14, and references therein).        
Carrier proteins are in particular used to improve the immunogenicity of antigens. Carrier proteins containing coiled coils have been described previously, notably a pentamer derived from COMP (15) and an artificial sequence which also forms pentamers (34), and heptamers derived from mammalian C4bp oligomerisation domains, such as the murine domain IMX108 (16), or avian C4bp oligomerisation domains (16, WO 2005/077976 and WO 2007/062819). A hybrid avian oligomerisation domain called IMX313 (WO 2007/062819) is used as an example here.